A chip guard ring typically comprises a stack of back-end-of-line (BEOL) metal interconnect structures that are located on an outer periphery of a semiconductor chip. The chip guard ring functions as a metal seal against ionic contaminants. The chip guard ring also functions as a low resistance path between electrical ground nodes of semiconductor devices on the semiconductor substrate and grounding metal pads located on the top surface of dielectric layers including back-end-of-line metal interconnect structures of the semiconductor chip. Typically, multiple grounding metal pads are required to provide adequate grounding of the semiconductor chip's guard ring. The grounding metal pads may be C4 flip chip pads or wirebond pads.
On one hand, an increase in the number of grounding pads on the guard ring provides enhanced grounding of the semiconductor circuit in a semiconductor chip. By providing sufficient electrical grounding, spurious signals on the guard ring and in the substrate around the guard ring area are blocked and the voltage at the electrical ground at the semiconductor chip is stabilized to provide higher performance. On the other hand, the number of the grounding pads on the guard ring needs to be minimized to reduce the size of the semiconductor chip because each grounding metal pad requires additional area for the semiconductor chip. The minimized number of the pads is also important to reduce the bonding cost of the chip package. Excessive reduction in the number of the grounding metal pads may result in degraded circuit performance through insufficient blocking of spurious signals to the guard ring electrical ground of the semiconductor chip. These two contradicting requirements make the design of a compact high performance semiconductor chip difficult.